1. Field of the Invention
The present invention relates to an image display apparatus for displaying on a screen or the like what is displayed on a display of a personal computer, what is displayed on a TV screen, a movie, or the like.
2. Related Background Art
These days, presentation materials prepared with a personal computer, what is displayed on a TV, a movie, or the like are often enlarged and displayed on a, screen or the like using an image display apparatus such as a liquid crystal projector. In this case, important information contained in the materials, on the display, or the like is often displayed in a specified region (generally, a central portion) of a displayed image. In a liquid crystal projector or the like, in order to emphasize important information, it is effective to increase the brightness (increase the contrast) of a region where the important information is displayed. In other words, important information often concentrates in a specified region of an image, and, in order to emphasize the important information, there is an increasing need for displaying the specified region of the displayed image at higher brightness.
Japanese Patent Laid-open Application No. 9-54279 proposes a method of displaying, with a liquid crystal projector, a central portion of an image at higher brightness than that of a peripheral portion. The disclosed method is as follows. An illumination optical system for illuminating an image forming element (a liquid crystal display panel in the case of a liquid crystal projector) comprises two fly-eye lenses. Respective lenses in each of the two fly-eye lenses all have the same focal length. Two of the respective lenses which overlap with each other in a direction of an optical axis makes a pair. The focal lengths of the lenses and the like are set such that a region of the image forming element illuminated with light through such pairs of the lenses is narrower than an effective region (a region where the image is formed on the image forming element). In the fly-eye lenses, since the positions of the respective lenses making a pair are slightly shifted from each other along the optical axis, the regions illuminated by the respective lenses making a pair are also slightly shifted from each other in a plane perpendicular to the optical axis. As a result, the illumination in the central portion of the effective region where more overlap of illumination occurs becomes higher than that in the peripheral portion of the effective region.
However, since such a structure is fixedly arranged in the illumination optical system, the illumination distribution of the illuminated image forming element can not be changed from the state where the central portion has the higher illumination. Therefore, there is a problem that, in case important information is also included in the peripheral portion of the image, for example, in case of a display of a personal computer, the information is difficult to view due to the lower illumination in the peripheral portion.